{"id":"CVE-2026-87121","aliases":["DEBIAN-CVE-2026-87121","EUVD-2026-84816","GHSA-h8q6-7rjx-3m2r","UBUNTU-CVE-2026-87121"],"status":"published","title":"Out-of-bounds write in lwIP TCP/IP Stack MQTT Client Application","description":"lwIP TCP/IP Stack MQTT is vulnerable to an out-of-bounds write, which may allow an attacker to gain full code execution on the device.","severity":{"version":"4.0","score":9.3,"vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N","level":"critical","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.00775,"percentile":0.56041,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":false,"fix_available":true},"cwes":["CWE-787"],"published":"2026-09-22T19:48:25Z","modified":"2026-10-17T13:01:14Z","fixes":[{"ecosystem":"Debian:14","package":"lwip","fixed_in":["2.2.1+dfsg1-8"],"sources":["osv"]}],"affected":[{"source":"osv","ecosystem":"Debian:12","package":"lwip","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.1.3+dfsg1-2","2.1.3+dfsg1-3","2.1.3+dfsg1-4","2.2.0+dfsg1-1","2.2.0+dfsg1-2","2.2.0+dfsg1-3","2.2.0+dfsg1-4","2.2.0+dfsg1-5","2.2.0+dfsg1-6","2.2.0+dfsg1-6.1","2.2.0+dfsg1-6.1~exp1","2.2.0+dfsg1-7","2.2.0+dfsg1-8","2.2.0+dfsg1-9","2.2.1+dfsg1-1","2.2.1+dfsg1-2","2.2.1+dfsg1-3","2.2.1+dfsg1-4","2.2.1+dfsg1-5","2.2.1+dfsg1-6","2.2.1+dfsg1-7","2.2.1+dfsg1-8"]},{"source":"osv","ecosystem":"Debian:13","package":"lwip","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.1+dfsg1-1","2.2.1+dfsg1-1+deb13u1","2.2.1+dfsg1-2","2.2.1+dfsg1-3","2.2.1+dfsg1-4","2.2.1+dfsg1-5","2.2.1+dfsg1-6","2.2.1+dfsg1-7","2.2.1+dfsg1-8"]},{"source":"osv","ecosystem":"Debian:14","package":"lwip","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.2.1+dfsg1-8"}]}],"versions":["2.2.1+dfsg1-1","2.2.1+dfsg1-2","2.2.1+dfsg1-3","2.2.1+dfsg1-4","2.2.1+dfsg1-5","2.2.1+dfsg1-6","2.2.1+dfsg1-7"]},{"source":"osv","ecosystem":"Ubuntu:Pro:20.04:LTS","package":"lwip","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.1.2-3","2.1.2-5.1","2.1.2+dfsg1-1","2.1.2+dfsg1-4","2.1.2+dfsg1-4ubuntu0.1~esm1"]},{"source":"osv","ecosystem":"Ubuntu:Pro:22.04:LTS","package":"lwip","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.1.2+dfsg1-8","2.1.2+dfsg1-9","2.1.3+dfsg1-1","2.1.3+dfsg1-1ubuntu0.1~esm1"]},{"source":"osv","ecosystem":"Ubuntu:Pro:24.04:LTS","package":"lwip","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.1.3+dfsg1-2","2.1.3+dfsg1-4","2.2.0+dfsg1-2","2.2.0+dfsg1-3","2.2.0+dfsg1-4","2.2.0+dfsg1-5","2.2.0+dfsg1-6","2.2.0+dfsg1-6.1","2.2.0+dfsg1-6.1build1","2.2.0+dfsg1-6.1build2","2.2.0+dfsg1-6.1ubuntu0.1~esm1"]},{"source":"osv","ecosystem":"Ubuntu:26.10","package":"lwip","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.1+dfsg1-4","2.2.1+dfsg1-5","2.2.1+dfsg1-7"]},{"source":"osv","ecosystem":"Ubuntu:Pro:26.04:LTS","package":"lwip","ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["2.2.1+dfsg1-2","2.2.1+dfsg1-3","2.2.1+dfsg1-4","2.2.1+dfsg1-4ubuntu0.1~esm1"]}],"products":[{"vendor":"lwip","product":"tcp/ip stack mqtt"}],"references":[{"url":"https://savannah.nongnu.org/projects/lwip","tags":["report"]},{"url":"https://www.cisa.gov/news-events/ics-advisories/icsa-26-265-01","tags":["report"]},{"url":"https://github.com/cisagov/CSAF/blob/develop/csaf_files/OT/white/2026/icsa-26-265-01.json","tags":["report"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-87121"},{"url":"https://github.com/advisories/GHSA-h8q6-7rjx-3m2r"},{"url":"https://security-tracker.debian.org/tracker/CVE-2026-87121","tags":["advisory"]},{"url":"https://ubuntu.com/security/CVE-2026-87121","tags":["report"]},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-87121","tags":["report"]}],"sources":{"cve":[{"id":"CVE-2026-87121","title":"Out-of-bounds write in lwIP TCP/IP Stack MQTT Client Application","description":"lwIP TCP/IP Stack MQTT is vulnerable to an out-of-bounds write, which may allow an attacker to gain full code execution on the 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